1. Field of the Invention
The present invention relates to a combustion chamber for gas turbine engines, particularly aircraft turbojet engines, which is constituted of an outer casing, at least one flame tube inserted therein, and incorporating at least one ignition device for the produced, respectively supplied fuel-air mixture.
In general, the following operating requirements are imposed on ignition devices for the combustion chambers of gas turbine engines:
1. l Starting condition (cold start); PA1 2. starting condition (hot start); as well as PA1 3. starting condition: reignition at high flight altitude (at about 20,000 to 30,000 feet).
2. Discussion of the Prior Art
Presently known ignition devices for combustion chambers will, as a rule, satisfy the abovemenioned conditions but with substantial limitations, and particularly with regard to the difference in the aerodynamic loading of the combustion chamber, in effect, meaning relatively strongly mutually deviating flow conditions in the region of the ignition zone of the combustion chamber.
For the starting condition (cold start), as a rule starting speeds about 10% of the rated rotational speed should be adequate. This requires a good ignition and heat release performance on the part of the combustion chamber. Experience has shown that the values for the temperature increase in the combustion chamber following the ignition sequence lie at T.sub.3 /T.sub.2 [K/K].apprxeq.2 to 3. Thereby, there will be avoided over-heating as well as thermal blockage of the turbines and attendant compressor surges. As is known, for a slowly ignitable combustion chamber, the then occurring lengthy ignition delay periods will lead, on the one hand, to inadmissibly high starting temperatures and, on the other hand, to aborted start (time-dependent fuel cut-off through a safety device).
The reignition of the combustion chamber at high flight altitudes of flight sets the highest demands on the ignition capability of the combustion chamber, as well as on the ignition devices. The problems of the starting condition "cold start" are applicable here in the same sense, but aggravatingly effective are the lower air and fuel temperatures, as well as the lower air pressure and the increased air speeds in the region of the combustion chamber ignition zone. A poorer ignition performance at elevated altitudes may, upon occasion, force the aircraft to drop to a lower altitude and may, under circumstances, additionally lead to excessively high ignition temperatures (automatic cut-off, aborted start).